PROJECT SUMMARY/ABSTRACT Obesity and its related comorbidities (diabetes, heart disease, hypertension, etc.) currently afflicts more than 114 million people in the United States and the absence of effective treatment options is reflected by the projected rise to nearly 150 million people by 2030. Excess caloric intake is the primary cause of obesity, however, the neural mechanisms driving superfluous food intake (and likely underlie the pathogenesis of obesity) remain unidentified. Previous studies in rodents consistently show that diets high in saturated fat and sugar increase excitability of neuronal circuits responsible for maintaining energy homeostasis. This increased excitability coincides with increased food intake, body-weight, and leptin insensitivity. However, the time course for these effects and the importance of underlying synaptic changes are unclear. These changes likely drive development and maintenance of diet-induced obesity, as well as difficulty losing weight or weight gain after weight loss. Agouti-related peptide (AgRP)/ neuropeptide-Y (NPY) neurons in the arcuate nucleus of the hypothalamus are the primary neuronal population responsible for food intake. AgRP neural activity rapidly and reliably initiates food seeking behavior, which is typically enhanced by fasting or caloric restriction and subsides upon initiation of meal consumption. Further, AgRP neuronal activity is consistently elevated following high fat diet (HFD) feeding. Our preliminary data suggest divergent effects of short- and long-term HFD on synaptic plasticity and signal integration to AgRP/NPY neurons. Specifically, short-term (2 day) HFD increases excitatory signaling to AgRP neurons. However, long-term (8 weeks) HFD results in sustained AgRP neural activity despite increased inhibitory signaling. Since the mechanisms underlying these effects remain poorly understood, my objective is to utilize previously mapped excitatory and inhibitory inputs to probe HFD-induced synaptic plasticity and AgRP neuronal activity. I will also use AgRP-specific RNA sequencing to identify transcriptional changes related to both short- and long-term HFD feeding. By pairing electrophysiology with an ?omics approach, I will identify a priori genes and prioritize novel candidate genes for validation studies in both short- and long-term HFD fed mice. These will focus on the reported alterations to excitatory or inhibitory inputs and phenotypic changes in feeding behavior and weight gain. Diet-induced alterations to neural mechanisms within the AgRP/NPY neuronal population, are crucial for understanding homeostatic dysregulation. Identification of the underlying mechanisms driving HFD-induced obesity are critical for future development of novel therapeutic strategies to combat diet-induced obesity. Overall, this research program proposes experiments that anticipate the discovery of previously undescribed stimulators of appetitive behavior following acute or chronic consumption of obesogenic diet.